Pulmonary surfactant is a complex material composed of several lipids and proteins bound together by non-covalent bonds. Physiological and physicochemical studies show that this material is rapidly metabolized, perhaps in response to physiological requirements, and that either a deficit or excess of this material in the alveolar spaces may be detrimental to good health. Disturbances in its metabolism and function are reflected in the etiologies of certain respiratory and cardiopulmonary diseases. This study will investigate the means by which the metabolism of pulmonary surfactant may be regulated, with particular attention to the metabolism of the apoproteins found in purified surface active material. Studies will be carried out in vivo, using immunological techniques specific for the apoproteins in this material, and in vitro, investigating the metabolism of the apoproteins in purified preparations of Type II alveolar epithelial cells. These results may provide insight into the molecular events associated with the synthesis and secretion of surfactants and lead to a better appreciation of the physiological functions of its apoproteins.